1. Field of the Invention
This invention relates to latex compositions or paint vehicles as they are sometimes referred for semi-gloss and flat interior paint compositions. Latex paint compositions have captured a significant portion of the indoor and outdoor paint market because they have several advantages as compared with the organic solvent type. Three significant advantages are: the paints offer an easy mechanism for cleanup, there is substantially no air pollution and there is a reduced possibility of fire hazard. On the other hand, the coating properties and storage stability of the latex paints have been somewhat inferior to those of the solvent type, particularly in obtaining desired film thickness and obtaining good adhesion.
Two types of emulsions commonly used in formulating latex paints include the all acrylic system, e.g., the systems using copolymerized methyl methacrylate, butyl acrylate, 2-ethylhexylacrylate with small proportions of acrylic acid, etc., as may be desired, and vinyl acetate formulations usually in combination with a small proportion of a lower alkyl acrylate, e.g., 2-ethylhexyl acrylate, methyl methacrylate or butyl acrylate. Heretofore, the all acrylic system has been used in premium quality paints as the emulsions have provided for good water resistance, desired leveling, film hardness, durability, scrubability, etc. The vinyl acetate-acrylic copolymer systems have been utilized in formulating interior flat and semi-gloss paints and exterior house paints, and the vinyl acetate-butyl acrylate latices result in paint films with excellent toughness, scrub resistance and durability, while the vinyl acetate-dibutyl maleate emulsions have good abrasion resistance and flexibility as well as durability.
Wet adhesion, i.e., the quality of adhering to a previously painted, aged surface under wet or moist conditions, has been imparted to both acrylic systems and vinyl acetate systems by polymerizing a wet adhesion monomer into the copolymer. Typically, these monomers have terminal olefinic unsaturation at one end, and a terminal ureido or urea functionality at the other end of the monomer. Although these monomers increase the ability of the emulsion to adhere to a previously painted film under moist conditions, these monomers sometimes have been difficult to polymerize into a system, particularly an acrylic system, and achieve other desired properties in the paints, thus wet adhesion of the paint vehicle is imparted by blending different kinds of acrylic polymer emulsions to obtain the overall properties desired in a paint vehicle, namely, durability, wet adhesion, scrubbability, flexibility, good leveling, abrasion resistance, toughness, etc.
2. Description of the Prior Art
Specific examples of acrylic and vinyl ester paint vehicle systems are shown in the following U.S. Patents.
U.S. Pat. No. 3,969,296 discloses a process for producing a vinyl acetate emulsion having improved adhesion characteristics against usual wet-cleaning with a cloth, sponge, etc. The emulsion is prepared by copolymerizing a small amount of a glycidyl ester of an alpha-beta ethylenically unsaturated acid with vinyl acetate followed by neutralization with ammonia.
U.S. Pat. No. 3,985,698 discloses an emulsion suited for improving the coating property and storage stability of emulsion paints by adding an amine, ammonia, or base solubilized acrylic resin produced by reacting a tertiary amine with an amino alkyl acrylate to a vinyl acetate or acrylic emulsion.
U.S. Pat. No. 3,563,944 discloses a colloid-free vinyl acetate emulsion suited for paint formulation having good scrub resistance, film forming properties, mechanical stability, etc. The copolymer consists of vinyl acetate and a lower alkyl acrylate, or an alkyl maleate. Enhanced stability is imparted by polymerizing a portion of the monomers in a colloid-free aqueous medium and then adding more monomer during the course of reaction and using a nonionic surfactant to stabilize the polymerization.
U.S. Pat. Nos. 3,369,008; 3,366,613; 2,940,950; 2,881,171; 2,727,019; 3,509,085; 2,980,652; and 3,356,654 disclose various paint emulsion systems which include a functional monomer for imparting wet adhesion to the emulsion. As noted in U.S. Pat. No. 3,509,085, one of the difficulties with many of the prior art latex paints was that they did not adequately adhere to previously painted surfaces which are glossy or chalky, and they did not adhere to surfaces previously painted with oil-based paints. By including a wet adhesion monomer such as described in the patents, the difficulty was overcome. In each of these patents, the functional monomer has vinyl unsaturation, except for U.S. Pat. No. 3,509,085, which has allylic unsaturation. All disclose terminal ureido functionality, e.g., a heterocyclic urea functionality such as an alkyl heterocyclic urea such as ethylene urea.